PHARMACOLOGICAL ACTIONHISMANAL* is a long-acting and selective oral histamine H1-antagonist.

Pharmacokinetic studies in man demonstrated that astemizole is rapidly absorbed, peak plasma concentrations being attained within 1 to 4 hours. The drug is extensively metabolised, and excreted as metabolites chiefly in the faeces. The half-life of the parent substance is approximately 1 day and the elimination half-life of the active metabolites is 10 to 14 days.

INDICATIONSHISMANAL* is indicated for the treatment of allergic rhinitis, allergic conjunctivitis and chronic urticaria.

CONTRA-INDICATIONSHISMANAL* is contra-indicated in patients with known intolerance to the drug or to any of the inactive ingredients.

Concomitant administration of an oral or parenteral formulation of ketoconazole, itraconazole, miconazole, erythromycin, josamycin or therapeutic doses of quinine with HISMANAL* is contra-indicated.

The recommended daily dosage should not be exceeded. Since HISMANAL* is extensively metabolized by the liver, the use of HISMANAL* in patients with significant hepatic dysfunctions should generally be avoided.

The safety of HISMANAL* in pregnant or lactating women has not been established.

DOSAGE AND DIRECTIONS FOR USE The recommended daily dosage should not be exceeded.

Children from 6 to 12 years: 5 mL (5 mg) of the suspension once a day. SHAKE THE SUSPENSION BEFORE USE.

Optimal absorption is achieved when HISMANAL* is taken on an empty stomach.

SIDE-EFFECTS AND SPECIAL PRECAUTIONS Mass gain may occur during prolonged treatment.

Headache, dizziness and nausea may occur.

Cases of hypersensitivity reactions such as angio-oedema, bronchospasm, photosensitivity, pruritus, rash and anaphylactoid reactions have been reported. There have also been isolated cases of convulsions, benign paraesthesias, myalgia/arthralgia, oedema, mood disturbance, insomnia, nightmares, transaminase elevations and hepatitis. In most cases, a causal relationship with HISMANAL* is unclear.

Drug interactions:HISMANAL* lacks significant sedative effects. Patients should, however, be warned that a small number of individuals may experience sedation. It is therefore advisable to determine individual response before driving or performing complicated tasks. This effect may be compounded by the simultaneous intake of alcohol or other central nervous system depressants.

The concomitant oral or parenteral administration of certain -azole antifungals, of certain macrolide antibiotics and of the therapeutic doises of quinine may decrease the metabolism of astemazole and result in elevated plasma levels. The use of such drugs with HISMANAL* is therefore contra-indicated.

In vitro studies further suggest that an interaction with azithromycin and clarithromycin is unlikely. The clinical relevance of this in vitro finding is not known as the possibility of an interaction with clarithromycin or azithromycin in the clinical situation has not been studied.

Patients known to have conditions leading to QT prolongation may experience QT prolongation and/or ventricular arrhythmias with astemizole. Therefore it is advisable to avoid its use in patients with a congenital QT syndrome; in patients who are taking medications which are reported to prolong the QT-interval (including anti-arrhythmics, terfenadine and erythromycin); or in patients with uncorrected hypokalaemia.

KNOWN SYMPTOMS OF OVERDOSAGE AND PARTICULARS OF ITS TREATMENTAlthough overdoses have been reported with no ill effects, rare cases of serious life-threatening cardiovascular adverse events including QT prolongation, torsades de pointes, and other ventricular arrhythmias have been observed in patients exceeding recommended doses of astemizole. While the majority of such events have occurred following substantial overdoses of astemizole, torsades de pointes (arrhythmias) have very rarely occured at reported doses of 20 - 30 mg daily (2 - 3 times the recommended daily dose).

In some cases, severe arrhythmias have been preceded by or associated with one or more episodes of syncope. Therefore, syncope in patients receiving astemizole should lead to immediate discontinuation of treatment and appropriate clinical evaluation, including electrocardiographic testing.

Supportive measures including gastric lavage and emesis should be employed, followed by the administration of activated charcoal. In these patients the ECG should be carefully monitored. If the QT interval is prolonged, the monitoring should continue as long as it remains prolonged. Appropriate anti-arrhythmic treatment may be needed, but treatment with anti-arrhythmics known to prolong QT interval should be avoided. Studies in patients with renal insufficiency suggest that haemodialysis does not increase clearance of the drug.